My grandson was in a museum gift shop and spotted some " Big Bang " cannons. The cannons that use carbide to produce acetylene. The price was not on the merchandize so he took one of the smallest to the clerk to find out the price. And he and I were both surprised when the price turned out to be $108.xx. He decided that was way too much money.
I thought I would make him a brass cannon for Christmas. So today I went to the local scrap yard and got some brass. _And this evening found a drawing on the internet of a 6 lb bronze field gun that I can scale to a size to fit the brass I bought. And I think I am good to go. But thought I would ask if anyone has some suggestions. I am curious how other people have dealt with the trunions. I am inclined to make them as separate parts and silver braze them on.
My grandson was in a museum gift shop and spotted some " Big Bang " cannons. The cannons that use carbide to produce acetylene. The price was not on the merchandize so he took one of the smallest to the clerk to find out the price. And he and I were both surprised when the price turned out to be $108.xx. He decided that was way too much money.
I thought I would make him a brass cannon for Christmas. So today I went to the local scrap yard and got some brass. _And this evening found a drawing on the internet of a 6 lb bronze field gun that I can scale to a size to fit the brass I bought. And I think I am good to go. But thought I would ask if anyone has some suggestions. I am curious how other people have dealt with the trunions. I am inclined to make them as separate parts and silver braze them on.
Will this be a functional item? If so then the easiest way to make it safe and would be to line the bore with a steel sleeve. Trunions could then be done very solid. Basically you would finish the exterior. Drill through the cannon, silver braze in the trunion shaft then bore the cannon barrel bore, Machine a sleeve and silver braze that in as well. With the steel you could also make a breech plug and attach it to the sleeve as well.
I don't think I would silver-solder a long steel tube to a long brass tube. The thermal coefficients are too different, and the thing will tear itself apart. What would work would be to thread the parts at one end and screw them together. But the steel tube must be able to move lengthwise.
If he's talking a carbide cannon the original manufacturer made some out of glass to show the safety of the design, and there's one on youtube made out of PVC pipe that has clearly been fired many times. Brass should be completely adequate. A carbide cannon makes a noise, it doesn't fire a projectile.
Just out of interest: If this were a functional item, made of brass, designed for black powder and firing projectiles, is there a formula relating the thickness of the barrel wall to the bore diameter? Does LaPlace's law apply here?
But what was being used as powder in it? The color did not look like either black powder or smokeless, so what was it? That would determine the peak pressure and thus the proper metal.
Don, many of the old, smaller cannons were made of brass, although it was closer to red brass (like that used in plumbing) than yellow brass. It was used for many swivel guns, for example.
One of my alloy books says that there wre over 300 named alloys called "brass" or "bronze" in the 1930s. But you're basically right -- tin bronze, also called "gun metal," is stronger than yellow brass, and has somewhat greater impact strength.
More than tensile strength, you need ductility and impact strength. Hell, the guns on the Monitor were made of cast iron, as were most guns of the time, with wrought-iron hoops on the breech to prevent castastrophic explosions. Even so, the gunnery officer would only load them to around 50% of their designed powder load. A big gun in that turret must have made them nervous.
Still, after 1,000 - 2,000 or so shots, some of those Civil War-era cannons would let go. It was a hazard of war.
Bronze is pretty sensitive to small variations in compositioin, in terms of elongation (ductility) and impact strength. I have the complete contemporary listings for compositions and properties, but I think you can find that stuff online these days.
Gun metal is what you want. It's around 10% - 12% tin, IIRC, with most of the rest copper. I'll look up the full composition if anyone is interested.
It's tricky to get into some of these fora. They do not let you into the topic, only to the front page. And they will not let me search. Most of the info I found so far relates to steel, the walls thickness at breech = bore diameter.
However, they did answer an unrelated question I was thinking about: The bore diameter = 39/40 x diameter of the projectile.
BTW, the "Gunmetal" listing in Wikipedia is screwed up. Don't rely on it. They say it's also called "yellow brass" in the US (it isn't), and then their reference, a UK web page, says it's called "red brass" in the US (it isn't).
Sheesh. I've never contributed to a Wikipedia listing, but this one needs some corrections.
Another Wikipedia entry (for "Brass") says in part:
====================================================================== "Red brass is both an American term for the copper-zinc-tin alloy known as gunmetal, and an alloy which is considered both a brass and a bronze. It typically contains 85% copper, 5% tin, 5% lead, and 5% zinc.[41][42] Red brass is also an alternative name for copper alloy C23000, which is composed of 14?16% zinc, 0.05% iron and lead, and the remainder copper.[43] It may also refer to ounce metal, another copper-zinc-tin alloy." ======================================================================
Among many other -- rather more intentional -- hazards of war.
And is there any practical way for the home machinist to tell what alloy they have? (Other than buying a certified alloy from a good vendor.)
We are about to embark on a confusing journey. When I was Materials Editor at _American Machinist_, I made the mistake of trying to learn all about these alloys. I remember an engineer at a copper company looked at me when I said that, and practically laughed his head off. 8-)
First off, cannons were cast, not wrought, and cast alloys are a bit different. Cast copper alloys' numbering begins at C8000, and there's the one called "red brass" in the plumbing-parts field, where most of it is used. Today, it is almost always leaded for fast and easy machining (the lead breaks chips; it doesn't really lubricate in copper alloys).
"Red brass" in general refers to copper alloys that typically contain
85% or more copper and no more than 5% or so zinc and 5% tin. Those are old small-cannon alloys.Today, they're used for industrial plumbing because of their good corrosion resistance. As far as I know, they aren't available today without lead. "Leaded red brass" casting alloy, C83600, is 85% Cu, 5% Sn, 5% Pb, 5% Zn.
"Gun metal," as it was used for cannons, also was cast. Today's cast gun metal, C90500, is 88% Cu, 10% Sn, 2% Zn. Another common name for it is Tin Bronze (there are several alloys called that). I've never heard it called red brass, but I never asked, either.
Wrought alloys are much more diverse. Here you really get into trouble with the common and commercial names. "Commercial bronze' (C22000) contains 90% copper, 10% zinc, and no tin at all. "Red brass" in a wrought alloy (C2300) is 85% copper, 15% zinc, no tin.
"Cartridge brass" (C26000) is 70% copper, 30% zinc. There are several alloys known as "yellow brass," but the average composition is
65% copper, 35% zinc.
And that's just the tip of the iceberg. A tip from an engineer I knew who works with this stuff: forget the terms "brass" and "bronze." They mean essentially nothing. The large majority of the "bronzes" available today contain no tin. Some "brasses" do. (All of the above comes from my non-ferrous bible, _Metals Handbook_, Ninth Edition.)
And if you're going to make a small cannon out of bar stock, stick with steel. Then you won't have to worry about Charpy impact strength, or stress-corrosion cracking, or any of the rest of the black magic associated with highly-stressed copper alloys.
And 360 brass is leaded for ease of machining, and plenty of don't run powder in this. :-)
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I've got a copy of _De Pirotechnia_ which includes how to sand cast a cannon barrel -- as well as the same for a bell. (Of course, almost everything is called by an obsolete name, making it more difficult to understand. And the lathes for boring a cannon once it is cast are interesting, too. :-)
Of course, the strength comes from the reinforcing of the chamber, not from the cartridge case material. :-)
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O.K.
Amen! (Not that I plan to do this -- but whoever the OP was apparently did intend to do so.
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